The present invention relates to an improved method and apparatus for enhancing chamber cleaning rates. More specifically, the present invention relates to a method and apparatus for enhancing the effective etch rate of a reactive chemical species which etches accumulated materials from processing chamber components.
The manufacture of liquid crystal displays, flat panel displays, thin film transistors and other semiconductor devices occurs within a plurality of chambers, each of which is designed to perform a specific process on the substrate. Many of these processes can result in an accumulation of material (e.g., material deposited on the substrate in layers, such as by chemical vapor deposition, physical vapor deposition, thermal evaporation, material etched from substrate surfaces, and the like) on chamber surfaces. Such accumulated material can crumble from the chamber surfaces and contaminate the sensitive devices being processed therein. Accordingly, process chambers must be cleaned of accumulated materials frequently (e.g., every 1-6 substrates).
To clean chamber surfaces, an in-situ dry cleaning process is preferred. In an in-situ dry cleaning process one or more gases are dissociated within the processing chamber to form one or more reactive gas species (e.g., fluorine ions, radicals). The reactive species clean chamber surfaces by forming volatile compounds with the material accumulated on those surfaces. Such an in-situ cleaning process reduces both particle counts and the system down time required for more interruptive cleaning processes which require the chamber to be opened.
Remote Plasma Source Cleaning (RPSC) is a further improvement to the in-situ plasma clean. In a RPSC, cleaning gas(es) are dissociated in a separate chamber, and the dissociated reactive species are then flowed downstream into the processing chamber where they clean/etch material from chamber surfaces. RPSC fully dissociates the cleaning gas and thus provides significant savings both monetarily and environmentally. In addition, RPSC reduces chamber consumables by eliminating the detrimental ion-bombardment associated with in-situ plasma cleaning processes.
Unfortunately, as described further below, both insitu cleaning and remote plasma source cleaning processes conventionally require considerable time and consume considerable amounts of cleaning gases, and thus undesirably increase the cost per substrate processed within a processing chamber. Further, in Remote Plasma Source Cleaning (RPSC) large cleaning rate variations often are observed between processing chambers cleaned by identical cleaning processes. Accordingly, there is a need for an improved method and apparatus for etching accumulated material from chamber surfaces.
The present inventors have discovered that chamber cleaning rates increase when chamber surfaces exposed to reactive cleaning gas species are mirror polished. Preferably the chamber surfaces are untreated, and most preferably are untreated aluminum. As used herein, an untreated chamber surface is one that has not been previously treated to enhance cleaning (e.g., by anodization or by applying a coating such as that disclosed in U.S. patent application Ser. No. 09/322,893, filed May 29, 1999). Such treated chamber surfaces already exhibit good cleaning rates. Mirror polishing is a process that reduces the surface roughness of a part, and therefore reduces surface area. The present inventors believe that mirror polishing achieves two goals, (i) reducing a part""s surface area so as to reduce the total number of sites at which the cleaning radical deactivation process occurs; (ii) removing surface contaminants which may otherwise bond with and reduce the number of cleaning radicals. Therefore, mirror polishing is believed to preserve cleaning radicals and render RPSC more effective.
The present invention comprises a system for processing substrates within a chamber and for cleaning accumulated material from chamber components. The system includes a processing chamber and a reactive species generator adapted to generate a reactive gas species for chemically etching accumulated material from chamber components, and at least one mirror polished surface or component which is exposed to the reactive species during the cleaning process. Preferably to have the greatest impact on chamber cleaning efficiency, the at least one mirror polished component(s) is a large component such as a gas distribution plate or a backing plate, and/or a plurality of smaller components (e.g., the chamber""s shadow frame, wall liners, susceptor, gas conductance line, etc.) so as to constitute a large percentage of the surface area exposed to the reactive species.
By mirror polishing surfaces exposed to the reactive species, not only have cleaning rate enhancements been observed, cleaning rate variations between processing chambers can be significantly reduced, process chamber throughput significantly increased and the amount of precursor gas required for cleaning reduced. Because of the high costs associated with precursor gases such as NF3, both monetarily and environmentally (e.g., global warming), any reduction in precursor gas consumption is beneficial. Moreover, mirror polished surfaces do not introduce any foreign material into the processing system, and do not present the adhesion problems experienced by most conventional surface treatments.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawing.